Storage of gas in underground excavation

ABSTRACT

Methods and systems for storing large volumes of gas, such as natural gas and the like, as commonly received from pipelines or tankers, in deep underground cavities under near-critical conditions of pressure and temperature. Part of the total gas received may be used to meet current requirements and the remainder stored during times of less than average demand, for use when demand is higher. Capital and operating costs of storing gas in ways disclosed make large scale storage attractive. As more gas is delivered from greater distances by more costly means, the need to accumulate gas in storage near markets, for use in emergencies and to keep the transportation system working at capacity, continually increases. This invention provides for this need, not only at attractive costs but also it provides a type of storage which can be built near many large markets where more conventional storage cannot; it requires little land and little surface construction. Gas is stored with maximum security and delivered with greatest availability.

Unite States atent n91 Loofbourow Nov. 19, 1974 1 1 STORAGE OF GAS 1NUNDERGROUND EXCAVATION [22] Filed: Mar. 1, 1971 [211 App]. No.: 119,623

[52] U.S. C1 62/260, 61/.5, 137/236, 165/45 [51] Int. Cl. F2541 23/12[58] Field of Search 61/.5; 137/236; 62/260, 62/54; 165/45 [56]References Cited UNlTED STATES PATENTS 2,316,495 4/1943 White 62/522,550,844 5/1951 Meiller et a1. 8/190 2,810,263 10/1957 Raymond 61/.52,932,170 4/1960 Patterson et a1... 61/.5

3,232,725 l/l966 Secord et al 48/190 3,298,805 I/l967 Secord et a148/190 OTHER PUBLICATIONS Distribution and Storage of Ethylene, W. H.Litchfield et al., Chemical Engr. Progress, April, 1959, pp. 68-73.

Primary Examiner-Meyer Perlin Assistant ExaminerRonald C. Capossela [57] ABSTRACT Methods and systems for storing large volumes of gas, suchas natural gas and the like, as commonly received from pipelines ortankers, in deep underground cavities under near-critical conditions ofpressure and temperature. Part of the total gas received may be used tomeet current requirements and the remainder stored during times of lessthan average demand, for use when demand is higher. Capital andoperating costs of storing gas in ways disclosed make large scalestorage attractive. As more gas is delivered from greater distances bymore costly means, the need to accumulate gas in storage near markets,for use in emergencies and to keep the transportation system working atcapacity, continually increases. This invention provides for this need,not only at attractive costs but also it provides a type of storagewhich can be built near many large markets where more conventionalstorage cannot; it requires little land and little surface construction.Gas is stored with maximum security and delivered with greatestavailability.

7 Claims, 6 Drawing Figures UNITS 0F JTA NDA RD GAS/UNIT JPA CE PAIENIL.I 91974 I 3. 848.427

sum 1 or 3 i -ue CRITICAL TEM ERATURE -2o0 450 #60 -5o 0 50 I00TEMPERATURE, "F

35 INVENTOR. v IPOBERTLZooFBouRoW H Arron/vs YJ' PATENIEL, NEW 1 9 I974sum 3 0F 5 \m SQ km INVENTOR. ROBERT L. LOOFBOUROW AT TORNEYS STORAGE OFGAS IN UNDERGROUND EXCAVATION This invention relates to the storage ofgas in underground chambers and more particularly to the undergroundstorage of gas at near-critical conditions.

Thermodynamically, the critical temperature of a gas is the temperatureabove which it cannot be liquefied at any pressure. The criticalpressure is the pressure of the saturated vapor at the criticaltemperature or the pressure at which the gas and liquid coexist at thecritical temperature. Gases and their mixtures deviate from the classicgas laws (which show the relation between pressure, volume andtemperature for an imagainary perfect gas) in that under some conditionsmore gas can be stored in a unit space than the gas laws indicate. Thisdeviation and its rate of change are most favorable to gas storage atthe critical temperature and pressure.

The compressibility factor of a gas is the measure of this deviation.For various elemental gases and gaseous chemical compounds, each at itscritical temperature and pressure, the compressibility factor is between0.3 and 0.19, that is, the volume of space occupied by a unit volume ofgas at critical conditions is between 0.19 and 0.30 of the volume whicha perfect gas would occupy at the same temperature and pressure.

The present invention is directed to the utilization of these propertiesfor the advantageous storage of gases and mixtures of gases undereconomically feasible conditions. The principal object of this inventionis to provide a storage system for large volumes of common andeconomically useful gases which can be built underground and used wherenatural underground reservoirs do not exist. The invention is directedespecially to the storage of large volumes of pure or mixed gases havingcritical temperatures lower than the freezing point of water. Data forsome of these gases are shown in Table l, appended.

The invention is illustrated in the accompanying drawings in whichcorresponding parts are identified by the same numerals and in which:

FIG. I is a diagram showing the number of units of standard methane gaswhich are contained in a space having a volume of one unit for a rangeof volume-pressure-temperature relationships;

FIG. 2 is a simplified and diagrammatic sectional view of an undergroundstorage system for the storage and temperature control of gas receivedat relatively high pressures and ambient temperatures;

FIG. 3 is a similar diagrammatic sectional view of a storage system forgas received liquefied at near atmospheric pressure and low temperature;

FIG. 4 shows a similar system with a warming coil in the storage chamberto gasify the stored liquid;

FIG. 5 is a partial sectional view showing immersion heating means inthe storage chamber; and

FIG. 6 is a diagrammatic sectional view of an excavated storage toreceive liquefied natural gas and warm it by natural heat exchange.

Whereas other known types of storage of these and similar gases utilize(a) high pressure to cram gas at ambient temperature into storage spacessuch as pressure tanks and conventional underground gas storagereservoirs, or (b) extreme low temperature to keep the gas liquid atnearly atmospheric pressure, this invention provides means of storinggas at optimum temperature and pressure, thereby enabling much more gasto be stored in a unit space and at moderate pressure. Whereas storageof these and similar gases in liquefied form requires facilities forliquefaction and revaporization, this invention provides a means ofstoring nearly the same amount of gas in a unit space without the costlyfacilities and energy consumption required to convert the stored gas toliquid and back again to gas. The inflexible requirement of extreme lowtemperature is also avoided.

The percentage of methane in natural gas is generally more than 85percent and may be 95 percent or more. When a mixture of gases is cooledand compressed sufficiently, liquid will condense. It will contain mostof the components of the gaseous mixture but their proportion in theliquid will not be the same as in the gas. Before natural gas has beenbrought to the ultra-dense condition here contemplated for storage, mostof the impurities with relatively high boiling points will have beenliquefied. Small percentages of butane, propane, ethane and carbondioxide may be present in the gas supplied by a pipeline and arerepresentative of this group. Depending on the composition of the gas asreceived, provision may be made to separate any fractions which liquefyas the gas is cooled. Impurities with relatively low boiling points,such as nitrogen, oxygen, hydrogen, helium and argon will not condense,though small amounts of these gases may dissolve in any liquids which doseparate.

For purposes of illustration, methane is used as an example, but it isevident that the same means can be used to store other gases, includingthose shown in Table l and others of similar properties.

Referring to the drawings, FIG. 1 shows the number of cubic feet ofstandard methane which can be stored in one cubic foot of space under arange of actual storage temperatures and pressures. Standard" gas is gasat standard conditions, 60 F and 14.7 psia. Study of these. curves willshow advantageous conditions for the storage of gas at a maximumpressure of about 50 atmospheres and within a temperature range fromabout to about F, or perhaps a little lower. Storage at this moderatepressure is especially useful because generally greater storagepressures require that underground storage excavations be at greaterdepths, which adds to construction cost and time. Note that 500 standardcubic feet can be contained in each cubic foot of excavated space atabout 50 atmospheres and at l60 F (Point A, FIG. 1), whereas if thetemperature were only 60 higher, that is l00 F, the pressure would haveto be increased to 320 atmospheres, if the same amount of gas were to becontained in the same space (Point B). Further, if the temperature were50 F, the storage pressure would have to be about 920 atmospheres toaccomplish the same result (Point C). (The data on the chart of FIG. 1is after Matschke, Donald E. and Thodos, George, The PVT Behavior ofMethane in the Gaseous and Liquid States, Jour. of Petroleum Tech., Oct.1960, pp. 67-71).

The solid line curves of FIG. 1 represent data in the gaseous phase. Thecurved dashed line through the critical point separates this from theliquid phase. Unless this dashed line is crossed, there is no change instate and only sensible heat, that needed to warm or cool the gas assuch, rather than to vaporize or condense it, is involved.

One principal object of this invention is to provide a type of storagefor large volumes of methane and similar gases, which can be built andused where conventional reservoirs do not exist. Underground storagesystems for the storage of gases at or near their critical temperaturesand pressures afford a number of advantages as compared with other typesof storage facilities which can be built at such places. Other andequally important objectives are (a) to provide an efficient way toreceive gas as liquid in large quantity rapidly, as from tankers; (b) towarm a part of the gas received and send it out more or lesscontinuously for consumption; and hold other gas in dense form to meetemergency or peak requirements.

1. The costs of construction and operation can be moderate because:

0. Many units of gas, made dense by low temperature and moderatepressure, can be stored in a unit of space without requiring the highpressures and consequent great depths that would be needed if gas werestored at ordinary temperatures. Where rock is reasonably favorable,this enables the storage excavations themselves to be made at costsfavorable as compared to the heavily insulated tanks of special metalsor alloys or insulated covered pits which may be used to store liquefiedgas at the surface. With favorable conditions it is possible to makespace for H5 or even l/lO of the cost of insulated tanks. The effect oflarge capacity in reducing the unit cost of underground excavations isgreater than in reducing those of surface storage tanks or pits.

b. Heat exchange and more common refrigeration units or compressor unitsof moderate capacity are substituted for the complicated largeliquefaction plants which are required where gas is to be liquefied forstorage as a liquid at approximately atmospheric pressure. To reduce thetemperature of a pound of methane gas from 60 F to l80 F at l,000 psirequires the absorption of 280 BTU. To reduce its temperature to "258 Fat atmospheric pressure and liquefy it, requires the absorption of 384BTU. Conversely the same amounts of heat must be restored in each caseto return the gas to 60 F. Heat exchange equipment for use with thedense gas will be comparatively compact.

c. Vaporizers are not needed if gas is stored as such.

Where it is stored as liquid at nearly critical temperature, the work ofvaporizing the liquid is less than if liquid has first to be vaporizedand then warmed from the temperature of liquid storage at atmosphericpressure (about l40 F below the critical temperature).

2. The critical temperatures of these gases are such that the walls ofthe excavations in which they are stored are surrounded by a thick shellof rock which remains below the freezing point of water, and some otherpossible contaminants, as long as the storage is in use. Any moisture inrock pores and fractures is frozen, sealing any possible leakage throughthe rock. In the unlikely event that rock at a chosen storage locus isboth permeable and dry, water or another suitable sealing material canbe placed in the rock through boreholes from the surface. As aconsequence, this type of storage can be built in many locations whichwould be questionable or unsuited to the construction of undergroundexcavations for the storage of gas under ordinary temperatures.

3. Like other types of deep underground gas storages, including the veryuseful conventional recharged natural gas reservoirs, this type ofstorage affords a degree of security distinctly superior to that of anystorage requiring extensive plant installations and storage tanks orpits at the surface.

4. Storage can be designed for expansion of capacity withoutinterruption of service, if and when required. Reference to FIG. 1 showsthat the quantity of gas which can be stored in unit space at atemperature of 120" F (235 standard cubic feet per cubic foot of space)may be more than doubled if the storage temperature is reduced to l60 Fwith no significant change of pressure (500 standard cubic feet percubic foot). Necessary but minor facilities, such as underground piping,can be built in anticipation of the change so that the only majoraddition would be the installation of additional heat exchange andrefrigerating equipment on the surface.

Depending on the manner in which gas is delivered to the storage, andhence on its condition at delivery, it is desirable that the equipmentprovided and even the design of the storage excavations be varied. Twocases are described under which it is assumed that gas is delivered as:

l. Compressed gas, ordinarily delivered from long distance pipelines atabout 700 to 1,200 psi and about 40 F to F, and

2. Liquefied gas, which may be delivered from tankers specially fittedout for the purpose, at substantially atmospheric pressure and about 260F.

EXAMPLE 1 STORAGE OF GAS RECEIVED AS COMPRESSED GAS In FIG. 2, there isshown schematically a system for the storage and temperature control ofgas received at relatively high pressure and ambient temperatures. Mostlong distance pipe lines deliver gas at pressures of 700 to 1,200 psi attempertures from about 40 F to 80 F. According to the system of thepresent invention, such gas is cooled at the surface to below itscritical temperature and then charged to the excavations at pressureswhich increase to the maximum storage pressure as the excavations fill.At maximum charge the pressure is slightly above the critical pressure.It is to be noted that the gas as it leaves the pipeline is likely to beat a pressure greater than the storage pressure; compression istherefore unnecessary. Because gas is stored as such, only sensible heatis involved; none is required for liquefaction or vaporization.

While gas is in storage some heat will come toward the storageexcavations from the surrounding rock mass. In order that the storageoperate as planned, the temperature of the stored gas must becontrolled, not so closely at the beginning and end of the storage cyclewhen the amount of the charge is relatively small, but narrowly nearmid-cycle when the charge is high.

Referring again to FIG. 1, allowable conditions within the storage arerepresented by the shaded area. While the storage contains less thanhalf the gas it may ultimately hold, conditions need not be controlledrigidly, but while the storage contains more than half its ultimatecharge, conditions must be kept between the maximum working pressure of50 to 55 atmospheres and the dashed line marking the border between gasand liquid phases. The latitude of temperature at lower pressures hasseveral advantageous consequences: (a) the heat exchanger-refrigerationplant does not need to have capacity to cool gas to the lowest storagetemperature at the highest charging rate; charging conditions may followany irregular path within the area indicated, and (b) if the storageoperates for a number of years within the area of greater latitude, itshould be possible to determine the heat conductivity of the walls ofthe excavations rather closely and so to select any additionalheat-exchanger-refrigeration equipment with confidence.

Referring now to FIG. 2, there is shown a storage excavation deep in theearth which is connected to the surface 11 by means of an input casing12 which extends through shaft 9 and a discharge casing or shaft 13. Theincoming gas is received through a pipeline 14 which is connected bymeans of a pipe 15 valved at 16 and by another pipe 17 valved at 18 to arefrigerating chamber 19. Another pipe 20 connects the refrigeratingchamber 19 with the input pipe 12, through expansion engine 21.Alternatively, the gas may bypass chamber 19 through pipes 22 and 23,valved at 24 and 25, respectively, or bypass chamber 19 and expansionengine 21 through pipes 22 and 26. Pipe 26 is valved at 27. Obviously,the gas may also be passed through chamber 19 while bypassing expansionengine 21.

An independent refrigerating system is provided at the surfacecomprising a compressor 28 driven by a suitable motor 29. The compressedrefrigerating gas from the compressor is conducted through a suitableconduit 30 to a condenser or cooling tower 31. A refrigerating coil 32in the chamber 19 is connected to the refrigerating plant by means ofpipes 33 and 34 which are fitted with valves 35 and 36, respectively.Valve 35 is an expansion valve. The cooling effect of the expanding gasflowing through the coil 32 in countercurrent flow against the incominggas serves to cool the gas to be stored as it is charged into thestorage excavation.

A further refrigerating coil 38 is optionally provided in the storageexcavation l0. Coil 38 is connected to the refrigerating plant at thesurface by means of pipes 39 and 40 passing down through shaft 9 andfitted with valves 41 and 42, respectively. Valve 41 is an expansionvalve. The cooling effect of the expanding gas flowing through coil 38functions to control the temperature in the excavation. Furthertemperature con trol means are provided in the form of a smallliquefaction plant 43 connected to the input pipe 12 by means of asuitable conduit 44 and connected to pipe 20 from the refrigeratingchamber by conduit 45. Conduits 44 and 45 are fitted with valves 46 and47, respectively.

A main valve 48 controls flow toinput pipe 12. The discharge pipe 13from the storage excavation is connected to a heater coil 49 housed in afurnace 50 or other heating chamber connected to a compressor 51 whichin turn is connected by means of a pipe 52 provided with a valve 53 toconnecting pipe 15 to the pipe line 14 which may also serve todistribute the stored gas from the excavation upon discharge.Optionally, discharge pipe 13 may be valved at 54 and bypass 55, valvedat 56, is provided to bypass the heat exchanger and pass gas directly tothe pump.

In the normal operation of the gas storage system of FIG. 2, gasreceived from pipeline 14 passes through pipe 15 and valve 16, throughpipe 17 and valve 18,

through chamber 19 where its temperature is lowered, and thence throughpipes 20, 23 and 26 and valves 25, 27 and 48 through input pipe 12 tothe storage excavation 10. In response to demand, the stored gas isdischarged through pipe 13. Optionally it is rewarmed in coil 49 inchamber 50. The discharging gas is pumped through compressor 51, pipe52, valve 53, pipe 15 and valve 16 back into pipeline 14 fordistribution.

During the storage cycle the temperature of the gas in the storageexcavation may be controlled by several means used either singly or incombination. These are as follows:

1. Gas may be circulated by being withdrawn from the storage excavation10, pumped up through pipe 13 through bypass 55 and pump 51, pipes 52and 17 and valves 53 and 18, recooled in the heat exchangerrefrigeration unit 19 and pumped back through pipe 20 and valve 48 andpipe 12 to the storage excavation. The design must be such that the gascirculates through all parts of the storage and should preferably permitthe direction of circulation to be reversed.

2. A refrigerated fluid from the surface is circulated through coil 38and pipes 39 and 40, using natural convection alone or with forcedcirculation. Although coil 38 is shown as connected to a refrigeratingplant for circulation of refrigerating gas, the same system mayoptionally be used for circulating a cooled fluid, such as brine, or thelike.

3. A small portion of the stored gas discharged from the refrigeratingchamber 19 on the surface is liquefied in the liquefaction plant 43 andinjected as a liquid to evaporate in the excavation and cool it.

4. In anticipation of gradual warming of the stored gas, depending onthe heat conductivity of the wall, to compensate for gradual warming,gas is introduced somewhat less than the critical temperature, to anextent that storage temperature will slightly exceed the criticaltemperature as the critical pressure is approached. Conversely, aftersomewhat more than half the gas has been withdrawn, the storage pressurewill drop, the remaining gas will be cooled by expansion countering theheat naturally conducted through the walls, thus reducing therequirements of temperature regulation as no large change of temperatureresults.

5. During the period of charging, and especially the early part of itwhen the pressure in the storage is low, gas to be charged is circulatedthrough engines 21, not only to recover power but to gain the maximumcooling effect from the expansion. As the amount of gas in storageapproaches its maximum and the storage pressure is closer to thepipeline pressure, gas is first cooled and then expanded through anengine.

6. The described means of temperature control may be supplemented byinsulating all or parts of the walls of the storage excavation as may bedesirable or necessary in view of the storage cycle and the nature ofthe rock mass surrounding the storage excavation.

7. The rock formation itself may contribute to temperature control wherethe excavations are made in cellular or other rock having less thanaverage conductivity. Sites may be selected with this in mind.

8. Some temperature control is achieved by use of compact storagechambers in order to reduce the ratio of rock surface to storage volume.

EXAMPLE'Z STORAGE OF GAS RECEIVED LlQUEFlED The choice between storingnatural gas as high density gas or as liquid and gas depends on thecondition of the gas as received by the owner of the storage and in viewof the heat transfer characteristics of the rock at the site or sitesavailable. If gas is received as liquid, as from tankers, and charged tostorage as liquid at only a little more than atmospheric pressure and atabout 260 F, the natural inflow of heat will gradually raise thistemperature. While both liquid and gas exist in the storage chamber, thepressure must equal the vapor pressure of the liquid at the temperatureexisting. If the storage is fully charged and then shut in for a longperiod, pressure might have to be controlled so that the planned workingpressure would not be exceeded. However, all rocks are poor conductorsof heat, some indeed being rather good insulators. Normal gaswithdrawals, even at low seasonal rates, may keep storage temperatureundesirably low. The natural heat inflow is allowed to warm the storedliquid so that it will vaporize, or may be vaporized more readily asrequired for withdrawal.

In FIG. 3, there is shown schematically a system for the storage andtemperature control of gas received as liquid at nearly atmosphericpressure. The storage excavation 60 deep in the earth is connected tothe surface by means of an input casing or shaft 61 and a dischargeshaft 62 through which a plurality of discharge pipes 63, 64 and 65extend. The incoming gas delivered from a marine or vehicular tanker ispumped rapidly through pipe 66 by pump 67 into the storage chamber 60through inlet 61. The liquefied gas may exist in the chamber both inliquid form, as at 68, and in gaseous form. inlet 61 is valved at 69.

The gas from storage is introduced for distribution to a pipeline 70.Gas in the vapor phase is withdrawn through pipe 63, which is valved at71, by pump 72 through pipe 73 to a heat exchanger 74 where the gas iswarmed, and thence to the pipeline. For temperature control of thestorage chamber, valve 75 may be closed and the warmed gas from heatexchanger 74 circulated back through pipe 76 either through pipe 64,which is valved at 77 and extends to a sump 78 in the liquid phase ofthe stored gas, or through pipe 65-, valved at 79, into the vapor phaseof the storage, both for the purpose of vaporizing more liquid forcirculating through pipeline 70.

The following means, singly or in combination, may be used forvaporizing gas in the storage chambers, or bringing it up to the desiredstorage temperature:

1. Warm methane, or any desired diluting gas is circulated into thegaseous or liquid phase. Circulation should be through all parts of thestorage and preferably the direction of circulation should bereversible.

2. A warmed fluid from the surface is circulated through heat exchangingcoils in the storage, the same coils being available for cooling, ifnecessary, as shown in FIG. 4.

A warm or cooling coil 80 is disposed in sump 78A in the liquid phase68A of the stored gas in chamber 60A. The structure for the introductionof gas into the storage and withdrawal of gas from the storage is shownin somewhat simplified form as described in connection with F IG. 3 withthe suffix A added to the reference numerals. Coil 80 is connected bymeans of a pipe 81 to pump 82 and pipe 83 to heat exchanger 84. Heatexchanger 84 may be for the purpose of either heating or cooling and isconnected to coil through pipe 85 and valve 86. The heating or coolingfluid, as necessary, is circulated in a closed system for heating orcooling the storage facility.

3. Electrically powered immersion heaters are placed through casedbore-holes into the liquid. As shown in FIG. 5, one or more immersionheating units 88 are disposed in the chamber 60B at least partiallysubmerged in the liquid phase of the stored gas. l-leater 88 isconnected by conductors 89 and 90 extending through a closed casing 91to an electrical heat generating source 92 at the surface.

4. To make heating most effective, its effect may be confined bybaffles, as also shown in FIG. 5. Vertical baffle 93 having one or moreopenings 94 adjacent the floor of chamber 60B confines the heat ofheater 88 to the compartment adjacent the discharge 638 to distributionpipeline 708 while still permitting inflow of colder stored gas to thatcompartment.

5. The pressure on the stored liquid may be reduced, thus lowering thetemperature at which it vaporizes.

6. Sites may be sought in granite or other more than normally conductiverock.

7. Storage chambers may be designed to afford a high surface to volumeratio, consistent with other design conditions.

It is also possible to displace liquid methane from the storageexcavations to the surface and vaporize it there. This can be donereadily by pumping warm methane gas into the storage, thus increasingthe pressure sufficiently to raise a column of liquid to the surface, orsimply by warming the storage to increase the pressure therein. Thedensity of methane is: at 1 16 F and 45.8 atmospheres, criticaltemperature and pressure, specific gravity of liquid and gaseous methaneis 0.162, density is 10.1 lbs. per ft. which produces a head of 70 psifor each 1,000 feet of vertical height.

at 263 F and 1 atmosphere specific gravity of liquid methane is 0.415,the density is 25.9 lbs. per ft. which produces a head of 180 psi foreach 1,000 feet of vertical height.

The storage of large volumes of natural gas and similar substances atlow capital and operating costs can be further improved by the use ofthe following additional means:

a. A number of separate storage chambers are provided as shownschematically in FIG. 6, which are so proportioned, oriented, disposedand so connected as to facilitate the maintenance of low temperature ina main storage chamber or chambers. A further means of cooling andmaintaining low temperature in the main storage is possible bycirculating cold gas or other fluid through chambers which are adjacentto but separate from the main storage chamber. This cold gas may be theexhaust from an expansion engine or other gas being prepared for sendingout and the chamber through which it is sent may be below the mainstorage to intercept heat flowing toward the surface.

b. Pipe from each chamber is generally brought through the shafts to thesurface but where convenient cased bore-holes are used which can bedrilled and connected to chambers without difficulty while the storageis in use.

0. For ease of operation and servicing, control valves are placed nearthe surface, preferably in closed pits.

For safety, excess flow valves are installed below the control valves.

d. Generally, for convenience in transferring gas, a slight pressuredrop is maintained between chambers through which gas moves, throughpumps or compressors can be installed for use where this may not bedesirable. For most dependable delivery, pressure in the final orsendout chamber should be higher than needed to move gas into thesendout pipeline.

e. Generally, gas-retaining bulkheads are placed in shafts and to reducethe pressure difference on them, they are filled above with sand, gasunder pressure or similar.

f. If incoming gas contains gases of higher boiling point than naturalgas, such as LPG, which tend to liquefy and separate in the storagechamber, a small pipe and pump is provided to remove the excessperiodically. However, within the range of conditions maintained in thestorage, the existence of a certain amount of LPG will increase thecapacity of the space to hold natural gas, which it absorbs. Either byallowing LPG to accumulate or by adding it, we have another way ofincreasing capacity. If any substantial amount of LPG moves through astorage system, there may be advantage in having a fractionating toweror other stripping device in the line between the first and secondstorage chambers as well as a separate small diameter pump column from asump in the first chamber.

Where gas is suppliedas aTit uid atafiroximy at mospheric pressure andabout 260 F, as from large tankers, these additional means are to beused:

g. The storage site is located as near as possible or practicable todeep water. This will decrease the cost of high capacity, speciallybuilt pipeline through which tankers are unloaded and also facilitatebarge shipment of stone. Beyond the storage, ordinary pipe can be usedand because it can be used continuously, its hourly capacity can be muchsmaller.

h. Where there is objection to charging LNG directly into storage, itmay be vaporized in the pipeline, sent through a grid of pipe buried inearth a few feet or submerged in a pond, sent through a coil in astorage chamber, or through a heat exchanging boiler with heat suppliedfrom warmed gas circulated from storage.

i. A number of separate chambers are provided through which gas iscirculated successively, being warmed gradually by natural heat flow,the chambers designed, oriented, connected and arranged to warm.

the gas most efficiently. The chambers are spread out horizontally toincrease heat exchange.

j. Natural warming issupplernented by providing heat exchangers on thesurface in any part of the system.

k. A final tempering chamber is provided from which gas can be sent outto consumption with least possible conditioning.

Referring now to F1616, there is shown diagrammat cally one above theother. The last is spaced horizontally from the others. Liquefied gas isdelivered periodically, as from tankers, for rapid unloading in line105. Line is provided with control valves 106, 107 and 108, asindicated. For use when needed, a line 109 containing pump 1 10 andcontrol valve 111 is provided to facilitate delivery of the liquefiedgas. A bypass line 112 including a heat exchanger 113, compressor 114and control valve 115 is provided where, for example, it may be'desiredthat the gas be vaporized or compressed before charging to the storagechambers.

"srarag'e' chamberwl 'is co'hne cted to the delivery line 105 throughlines 116 and 117 fitted, respectively, with control valves 118 and 119,and preferably, for safety, with excess flow valves 120 and 121. Chamber103 is connected with delivery line 105 by means of .line 122 fittedwith control valve 123 and excess flow valve 124. Chamber 102 isconnected with the delivery line by lines 125 and 126 fitted,respectively, with control valves 127 and 128 and excess flow valves 129and 130.

The gas from storage is circulated to a distribution line 131. Thedistribution line includes a heat exchanger 132 and desirably adehydrator 133, and is fitted with control valves 134 and 135. A bypassline 136 connected to an expansion engine 137 and fitted with controlvalve 138 is provided for use when desirable. Chamber 102 and chargingline 126 are connected with the distribution line 131 by means of line139 fitted with control valve 140 and excess flow valve 141. Chamber 103is connected with the distribution line through line 142 fitted withcontrol valve 143 and excess flow valve 144. Chamber 104 is connectedwith the delivery-distribution system through line 131 and lines 145 and146 fitted, respectively, with control valves 147 and 148 and excessflow valves 149 and 150.

Ordinary routing of the liquefied gas is in sequence to chamber 101 andthen to chambers 102, 103 and 104. By pumping, pressure in chamber 101may be kept the highest. However, valving and compressors allowflexibility. For more rapid warming, chamber 102 may be spacedhorizontally from chamber 101 instead of vertically.

Various alternative procedures are possible. The liquefied natural gasmay be pumped directly to chambers 101, 102 or 103 or to the heatexchanger 113 and compressor 114 and then to chambers 101, 102 or 103.Gas from chamber 101 may be drawn directly to chamber 102 or to chamber103. Gas from chamber 101 may be transferred directly or through theheat exchangercompressor to chambers 102 or 103 or returned to chamber101. Gas from chambers 102 and 103 may be transferred to the dehydrator133, heat exchanger 132 and expansion engine 137 to distribution to adistribution system or gas from chambers 102 or 103 may be transferredto chamber 104. Gas from chamber 104 may be transferred to thedehydrator-heat exchangerexpansion engine to distribution.

It is apparht that many modifications and variationsof this invention ashereinbefore set forth may be made without departing from the spirit andscope thereof. The specific embodiments described are given by way ofexample only and the invention is limited only by the terms of theappended claims.

TABLE 1 CRITICAL DATA FOR VARIOUS GASES Crit. Temp. Crit. Pres. Crit.Vol. Std. Vol. Ratio F Atmos. Cu. FL/pcr lb. (u. Ft./pcr lb. Std.VoL/Crit. Vol.

Argon 187.7 48.0 0.03 9.50 317 Carbon Monoxide. 220.3 34.5 0.053 13.57256 Hydrogen 399.8 12.8 0.516 188.6 365 Methane, CH, 116.5 45.8 0.09923.6 239 Nitrogen 232.8 33.5 0.053 13.57 256 Nitric Oxide, NO 136.7 65.00.031 12.66 408 Oxygen 181.8 49.7 0.037 11.87 320 Air 220.3 37.2 0045713.08 286 Natural Gas 1 37.4 46.l Z 96.3 45.7 3 1 18.6 45.3

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of storage of pipeline gas received as 2 compressed gas froma pipeline at pressures between about 700 to 1,200 psi and temperaturesbetween about 40 to 80 F in an excavated underground storage facilityincluding at least one excavated underground rock chamber, which methodcomprises:

A. cooling said gasto about -50 to -l50F and charging to said storagefacility at pipeline pressures,

B. when said facility contains about one half of its maximum capacity,increasing the pressure and maintaining at moderately elevated level upto about 2,500 psi,

C. maintaining the facility at reduced temperature between about -50 andl50 F, whereby the gas is maintained for storage predominantly in thegaseous state and is densified to store between about 75 and 475 cubicfeet of gas to each cubic foot of storage space,

D. circulating stored gas to heat exchangers at ground surface to coolthe gas to maintain the storage temperature,

E. discharging said stored gas upon demand, and

F. after the quantity of stored gas has been reduced to about one halfof its maximum, decreasing the pressure while maintaining thetemperature between about +50 and -l50 F.

2. A method according to claim 1 further characterized in that thestored gas is cooled by absorption of heat in said heat exchangers byexpansion of incoming gas from pipeline pressure to sendout trunklinepressure.

3. A method according to claim 1 further characterized in that thestored gas is cooled by absorption of heat in said heat exchangers byexpansion of incoming gas being charged to storage from pipelinepressure to storage pressure.

4. A method according to claim 1 further characterized in that gas iswithdrawn from the top of said chamber and cooled gas is reintroduced atthe bottom of said chamber.

5. A method according to claim 1 further characterized in that:

A. said storage facility comprises a plurality of storage chambersconnected in series, and B. the pressure in each of said storagechambers downstream from the first chamber is maintainedat a level lowerthan the pressure in the next adjacent upstream chamber.

6. A method according to claim 1 further characterized in that:

A. said gas to be stored is natural gas,

B. a small amount of liquefied petroleum gas (LPG) is maintained in saidstorage chamber, and

C. a portion of said natural gas is absorbed in said LPG, therebyincreasing the capacity of said chamber.

7. A method of storage of pipeline gas received as compressed gas from apipeline at pressures between about 700 to 1,200 psi and temperaturesbetween about 40 to F in an excavated underground storage facilitycomprising at least one excavated underground rock storage chamber and aplurality of other chambers adjacent to but separated from said storagechamber, which method comprises:

A. cooling said gas to about 50 to l50F and charging to said storagechamber at pipeline pressures,

B. when said storage chamber contains about one half of its maximumcapacity, increasing the pressure and maintaining at moderately elevatedlevel up to about 2,500 psi,

C. maintaining the storage chamber at reduced temperature between about50 and l50 F, whereby the gas is maintained for storage predominantly inthe gaseous state and is densified to store between about 75 and 475cubic feet of gas to each cubic foot of storage space,

D. circulating a heat exchanging fluid through said other separatedchambers to maintain the storage temperature within said storagechamber,

E. discharging said stored gas upon demand, and

F. after the quantity of stored gas has been reduced to about one halfof its maximum, decreasing the pressure while maintaining thetemperature between about +50 and F.

" UNITED STATES PATENT OFFICE (5/69) v CERTIFICATE OF CORRECTION PatentNo. 3 ,848 ,427 Dated November 19, 1974 Inventor) Robert L. LoofbourowIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

15 the title, "EXCAVATION" should be pluralized.

Column 7, line 61, "warm" should be --werming.

Column 9 line 5 "through" (second occurrence) should be --though--.

Signed and sealed this 14th day of January 1975.

(SEAL) Attest:

McCOY M. GIBSON. JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents

1. A method of storage of pipeline gas received as compressed gas from apipeline at pressures between about 700 to 1,200 psi and temperaturesbetween about 40* to 80* F in an excavated underground storage facilityincluding at least one excavated underground rock chamber, which methodcomprises: A. cooling said gas to about -50* to -150*F and charging tosaid storage facility at pipeline pressures, B. when said facilitycontains about one half of its maximum capacity, increasing the pressureand maintaining at moderately elevated level up to about 2,500 psi, C.maintaining the facility at reduced temperature between about -50* and-150* F, whereby the gas is maintained for storage predominantly in thegaseous state and is densified to store between about 75 and 475 cubicfeet of gas to each cubic foot of storage space, D. circulating storedgas to heat exchangers at ground surface to cool the gas to maintain thestorage temperature, E. discharging said stored gas upon demand, and F.after the quantity of stored gas has been reduced to about one half ofits maximum, decreasing the pressure while maintaining the temperaturebetween about +50* and -150* F.
 2. A method according to claim 1 furthercharacterized in that the stored gas is cooled by absorption of heat insaid heat exchangers by expansion of incoming gas from pipeline pressureto sendout trunkline pressure.
 3. A method according to claim 1 furthercharacterized in that the stored gas is cooled by absorption of heat insaid heat exchangers by expansion of incoming gas being charged tostorage from pipeline pressure to storage pressure.
 4. A methodaccording to claim 1 further characterized in that gas is withdrawn fromthe top of said chamber and cooled gas is reintroduced at the bottom ofsaid chamber.
 5. A method according to claim 1 further characterized inthat: A. said storage facility comprises a plurality of storage chambersconnected in series, and B. the pressure in each of said storagechambers downstream from the first chamber is maintained at a levellower than the pressure in the next adjacent upstream chamber.
 6. Amethod according to claim 1 further characterized in that: A. said gasto be stored is natural gas, B. a small amount of liquefied petroleumgas (LPG) is maintained in said storage chamber, and C. a portion ofsaid natural gas is absorbed in said LPG, thereby increasing thecapacity of said chamber.
 7. A method of storage of pipeline gasreceived as compressed gas from a pipeline at pressures between about700 to 1,200 psi and temperatures between about 40* to 80* F in anexcavated underground storage facility comprising at least one excavatedunderground rock storage chamber and a plurality of other chambersadjacent to but separated from said storage chamber, which methodcomprises: A. cooling said gas to about -50* to -150*F and charging tosaid storage chamber at pipeline pressures, B. when said storage chambercontains about one half of its maximum capacity, increasing the pressureand maintaining at moderately elevated level up to about 2,500 psi, C.maintaining the storage chamber at reduced temperature between about-50* and -150* F, whereby the gas is maintained for storagepredominantly in the gaseous state and is densified to store betweenabout 75 and 475 cubic feet of gas to each cubic foot of storage space,D. circulating a heat exchanging fluid through said other separatedchambers to maintain the storage temperature within said storagechamber, E. discharging said stored gas upon demand, and F. after thequantity of stored gas has been reduced to about one half of itsmaximum, decreasing the pressure while maintaining the temperaturebetween about +50* and -150* F.